Current and future therapeutic approaches in progressive supranuclear palsy

A Review of Treatment Options for Progressive Supranuclear Palsy

Progressive supranuclear palsy (PSP) is an atypical parkinsonian condition characterized by a symmetric akinetic-rigid syndrome, early falls, supranuclear gaze palsy, and a frontotemporal behavioral syndrome. The typical phenotype is termed Richardson's syndrome, but numerous other phenotypes have been described. The pathophysiology of PSP is not fully understood, but dysfunction of the tau protein seems to play a central role. Despite exciting new knowledge on the pathophysiology of PSP, there is still no highly effective symptomatic or disease-modifying treatment. We review the evidence on pharmacotherapy and experimental therapies in PSP and provide levels of recommendation for the off-label use of commonly used drugs in this disorder.

Disease-Modifying Treatments for Progressive Supranuclear Palsy

In recent years, research has focused on the development of disease-modifying treatments for PSP, targeting mainly at tau dysfunction. However, the glycogen synthase kinase 3 inhibitor, tideglusib, and the microtubuli stabilizer, davunetide, both failed to show efficacy in recent double-blind, placebo-controlled studies. Despite these results, further agents targeting tau dysfunction, tau post-translational modifications, or aiming at mictorubuli stabilization are currently being investigated. Further approaches under development include agents to reduce tau levels extracellularly by active or passive immunization, antisense oligonucleotides to reduce tau concentrations, and small interfering RNAs to suppress human tau expression. However, the major limitation on the way to find disease-modifying treatments for PSP still remains the lack of biomarkers. Indeed, for all of these potential therapeutic modalities, a well-designed human trial would require validated biomarkers, without which the results of negative efficacy trials will be difficult to interpret. In this regard, PET imaging using tau-specific ligands may be proven useful in the near future. There is great hope that the next decade will bring the first effective therapy for PSP.

Intrinsic connectivity network disruption in progressive supranuclear palsy

OBJECTIVE

Progressive supranuclear palsy (PSP) has been conceptualized as a large-scale network disruption, but the specific network targeted has not been fully characterized. We sought to delineate the affected network in patients with clinical PSP.

METHODS

Using task-free functional magnetic resonance imaging, we mapped intrinsic connectivity to the dorsal midbrain tegmentum (dMT), a region that shows focal atrophy in PSP. Two healthy control groups (1 young, 1 older) were used to define and replicate the normal connectivity pattern, and patients with PSP were compared to an independent matched healthy control group on measures of network connectivity.

RESULTS

Healthy young and older subjects showed a convergent pattern of connectivity to the dMT, including brainstem, cerebellar, diencephalic, basal ganglia, and cortical regions involved in skeletomotor, oculomotor, and executive control. Patients with PSP showed significant connectivity disruptions within this network, particularly within corticosubcortical and cortico-brainstem interactions. Patients with more severe functional impairment showed lower mean dMT network connectivity scores.

INTERPRETATION

This study defines a PSP-related intrinsic connectivity network in the healthy brain and demonstrates the sensitivity of network-based imaging methods to PSP-related physiological and clinical changes.